The invention relates to a method and system for generating laser pulses having a predefined amplitude, phase or polarization.
The invention of femtosecond lasers and the development of pulse shaping techniques opened the wide field of coherent control [1, 2]. The implementation of a pulse shaper into a feedback loop makes it possible to find the optimal pulse form for the investigated system without having any knowledge about the underlying physics [3]. By analyzing the obtained pulse shapes, the excitation process can be revealed. This powerful method was applied to many successful experiments in different fields [4]. In these experiments, the pulses were modulated in phase and/or amplitude. Since the majority of quantum systems are three dimensional, the vectorial component of the electrical field, the polarization, has to be considered additionally. Pulse shapers which are capable of polarization shaping were developed. The first attempts at polarization shaping employed standard double liquid crystal arrays which have their optical axes oriented at ±45° in the Fourier plane of a 4-f line [5]. The experimental implementation of this setup in a closed-loop experiment on optimizing the ionization of K2 and I2 showed nicely the relevance of the vectorial character of the light [6, 7]. Yet, in this setup the polarization control is limited to ellipses with fixed orientation. This limitation was overcome by additionally passing an array with its optical axis parallel to the input polarization in an 8-f geometry [8]. A four-array modulator was used to correct the polarization mode dispersion in optical fibers [9]. However, all these setups are not able to modulate the amplitude of the laser pulse. By passing through several liquid crystal arrays with appropriately aligned optical axes, the amplitude of the laser pulse is additionally shaped [10].